The invention relates to apparatus and methods for providing controlled exothermic chemical reactions which produce a heat output of a predetermined, controlled duration and intensity. Particularly, the invention relates to apparatus which produce heat by use of controlled exothermic chemical reactions.
The oxidation of alcohols and the associated liberation of heat energy during the oxidation reaction is well documented. The number of oxidizing agents available to oxidize alcohols is quite extensive, yet the most common oxidizing agents are those comprising manganese and chromium. For instance, primary alcohols can be oxidized into carboxylic acids, usually by heating with aqueous potassium permanganate. Alternatively, potassium chromate may be used to oxidize primary alcohols into aldehydes, which are in turn readily oxidized to acid.
Additionally, secondary alcohols may be oxidized to ketones by a variety of agents; for instance, by chromic acid, aqueous potassium chromate (K.sub.2 Cr.sub.2 O.sub.7), chromium sesquixoide in glacial acidic acid or chromium dioxide (CrO.sub.2) in pyridine.
However, use of exothermic oxidation reactions to provide heat under controlled conditions is fraught with a number of inherent difficulties. For instance, common oxidizing agents are strong oxidizers and may produce a fire hazard if not properly contained in a controlled environment. Also, the reaction rate of oxidation reactions may be very rapid, thus producing an instantaneous and intense release of heat when the oxidizing agent and the fuel come in contact.
In light of these difficulties, it is important that precise control and containment of the intensity and duration of the reaction be obtainable and available. To provide such control, we have determined that the oxidizing agent and the fuel must be selectively exposed to each other in amounts which both produce a specific, calculated amount of heat evolution and also react in a sustained and controlled fashion without combustion or extreme fluctuations in heat evolution. Thus, by controlling the exposure of the reactants to each other the rate, intensity and duration of the chemical reaction may be controlled. Particularly, when the use of an exothermic chemical reaction is desirable for use in conjunction with a heating device, preferably a food heater, the control and containment of the chemical reaction achieves an even greater importance.
To provide optimal heating characteristics for a food heater, a chemical heater should have the following attributes: (1) the heater should have a high heat output per unit mass of reactants; (2) the reaction rate of the reactants should be easily controllable over a wide range of times and temperatures; and (3) the reactants should have as their major component a liquid such that heat transfer is optimized between the heat provided by the reaction and the material to be heated by conduction. These particular attributes are provided by a controlled exothermic chemical reaction.
Accordingly, it is one object of this invention to provide a novel method of providing a controlled exothermic chemical reaction and the use of such a method in conjunction with a heating apparatus. Another object of this invention is to provide a food heater which provides a controllable and accurate rate of heat input to the material to be heated.